The present invention relates to an apparatus for separating hulled pistachio nuts from unhulled pistachio nuts.
Pistachio nuts have a hard shell around the edible nut and a pericarp or hull which encases the shell. The hull of unripened pistachios adheres strongly to the shell and is difficult to remove whereas the hull is relatively easily removed from ripe pistachios. It is necessary to mechanically hull pistachios in order to process commercial quantities of the nut.
The hulling of pistachios presents unusual problems of difficult solution. The hulls of pistachios are stronger, more tenaciously adherent to the shells, and more difficult to remove than the hulls of many nuts, particularly if the pistachio is not yet ripe. If the hull is not promptly removed from pistachios after harvest, it discolors the shells requiring that the normally attractive straw colored shells be colored to hide undesirable stains. For this reason, most commercial pistachios are dyed an unnatural and undesirable pink or red color to obscure the stains. Even when abundant hand labor is available, it is usually not feasible to hull sufficiently large volumes of pistachios soon enough after harvest to avoid shell discoloration. As a result, mechanical dehullers of various configurations have been developed. However, the dehulling apparatuses are designed to dehull only those pistachios which are easily dehulled, otherwise, the machines could damage the pistachios. Many pistachios are left with the hull intact or still clinging to the shell, particularly unripe pistachios. It is a laborious job to sort hulled pistachios from unhulled pistachios manually.
Therefore, there is a need in the art for an automated process and system for separating hulled pistachios from unhulled pistachios.
In general term, the invention provides a method and apparatus for separating unhulled pistachios from hulled pistachios. The pistachios are deposited onto the outside surface of the upper half of a rotating drum, on a portion of the drum where the outer surface is ascending. Pistachios which contact the drum are pulled upward by the rotation of the drum and pulled downward by the force of gravity. If the upward force overcomes the force of gravity, the pistachio will be pulled over the top of the drum and deposited on the other side.
A pistachio hull is more adhesive than a pistachio shell, which is relatively harder and smoother, particularly when the hull is damp. Therefore, if the drum rotates at a sufficient rate, unhulled pistachios and pistachios with the hull or a portion of the hull still attached will tend to be pulled upward by the rotation of the drum while hulled pistachios will tend to slide down the drum surface and not be pulled up and over the drum to the descending half side of the drum.
One skilled in the art will realize that the apparatuses and methods disclosed herein may be adapted to separate other nuts, berries or beans, where ripe and unripe (or desired and undesired) nuts, berries or beans have different coefficients of friction with the rotating surface of the drum. Further, the apparatuses and methods of the present invention may be used to separate such items from impurities such as branches, twigs, leaves if such frictional differences exist.
In one aspect of the invention, the invention comprises an apparatus for separating unhulled pistachios and hulled pistachios comprising:
(a) a support frame;
(b) a substantially cylindrical, horizontal drum rotatably mounted to the frame and having an ascending portion and a descending portion;
(c) means for rotating the drum; and
(d) means for depositing a mixture of hulled and unhulled pistachios onto the ascending portion of the drum.
In one embodiment, the pistachio depositing means comprises a conveyor supported by the frame and having a first end and a second end, wherein said second end is adjacent to the ascending portion of the drum, wherein pistachios are deposited on the first end, transported to the second end and deposited onto the rotating drum therefrom.
In another aspect, the invention may comprise an apparatus for separating unhulled pistachios from hulled pistachios comprising:
(a) a rotating drum having an outer surface which frictionally engages unhulled pistachios preferentially to hulled pistachios; and
(b) means for depositing pistachios onto the outer surface of the rotating drum on an upper portion of the drum where the outer surface is ascending.
In another aspect, the invention may comprise a method of separating unhulled pistachios from hulled pistachios comprising the steps of:
(a) providing a rotating drum having an outer surface which frictionally engages unhulled pistachios preferentially to hulled pistachios; and
(b) depositing pistachios onto the outer surface of the rotating drum on an upper portion of the drum where the outer surface is ascending;
(c) collecting unhulled pistachios from the descending half side of the drum; and
(d) collecting hulled pistachios from the ascending half side of the drum.